You cannot have a higher valor rank than your level, with the exception at 55 you can get your valor level to 100.
As long as you do a couple of WZs while you are questing you should be able to keep pace between your valor and level so when you hit 40 you can start trading in your WZ comms for RWZ comms. You can gauge how much your valor bar goes up each match, in pre-55s it is usually 1/8 - 1/4 per match depending on how many votes you got.
Thank you! This is very helpful. When I hit 30 and my valor dinged, it made me realize I hadn't been keeping track at all of how quickly I was gaining it.